"It appears that the testing procedures to clear horses for import from equine piroplasmosis countries have allowed infected horses to enter the United States," said Dr Dave Fly, state veterinarian for New Mexico.
Dr Fly was commenting in an update on the situation surrounding the disease, for which there is no known cure in horses.
His comments came after three racehorses destined for a New Mexico race meeting were tested and found to be positive for the disease.
The disease, which causes blood-loss anaemia, debilitation and sometimes death, is primarily transmitted by certain species of ticks.
However, other mechanical vectors such as biting insects, needles, tattoo instruments, contaminated serum and blood products are capable of transmitting the parasite.
Dr Fly said the current Texas outbreak appears to be tick transmitted, whereas previous recent outbreaks appear to have been related to transmission by way of mechanical means.
"The United States has been considered free of equine piroplasmosis since the mid-1980s," he said.
"The free status was reached after the expenditure of well over $US12 million of state, federal and industry dollars to eliminate the parasite from Florida.
"During the last two years, outbreaks have occurred in Florida, Missouri and Kansas.
"These outbreaks have been traced to high-risk horse racing on non-sanctioned race tracks.
"A sero-prevalence study recently conducted by the US Department of Agriculture shows that a low level of equine piroplasmosis does exist in the United States.
"Currently the state of Texas is experiencing an outbreak. At this time the outbreak is centered in Kleberg County Texas, but exposure and positive horses have been found in 14 states and several other counties in Texas.
"The true extent of the outbreak is unknown at this time.
"The New Mexico Livestock Board, in co-operation with the New Mexico Racing Commission, has entered into a proactive programme to protect the New Mexico racing industry as well as the New Mexico exhibition and breeding industry from the introduction of equine piroplasmosis into the New Mexico equine industry.
"Currently all horses entering New Mexico from Texas are required to present a negative Equine Piroplasmosis test.
"In addition, all horses entering a New Mexico racetrack are required to show evidence of a negative equine piroplasmosis test."
Dr Fly said the three horses that tested positive were destined to race at Sunland Park.
"These piroplasmosis-affected horses have not entered the race track," he said.
The animals were detected through the state's equine piroplasmosis racetrack screening programme. Over 1300 animals have been screened for the disease.
In its report on the New Mexico outbreak to the World Organisation of Animal Health, the USDA's Dr John Clifford said: "Preliminary results of the investigation indicate that the transmission of the organism may have resulted from management practices (use of shared needles or substances between horses) rather than by a tick vector.
He continued: "The New Mexico detections are not epidemiologically linked to the Texas equine piroplasmosis outbreak."
Dr Fly said horses considered at high risk are: